1. Field of the Invention
The present invent ion relates to an electronic circuit apparatus and, more particularly, to an electronic circuit apparatus which is formed by laminating a plurality of thin films onto an insulative substrate, and in which an electronic circuit device having two conductive layers which are laminated through an insulative layer is formed.
The invention is preferably used in an image reading apparatus for reading image information such as a character and graph provided in an information processing device of a facsimile or image scanner.
2. Related Background Art
In recent years, a long-shaped contact type image reading apparatus having an equal magnification optical system has been developed to realize the miniaturization and high performance of a facsimile, an image reader, or the like. Hitherto, such an image reading apparatus has been constructed such that signal processing ICs (integrated circuits) each consisting of a switching element and the like are connected to respective photoelectric converting elements arranged in an array of one line.
However, for the number of photoelectric converting elements, 8 elements per 1 mm, for example, 1728 elements for A4 size are necessary in accordance with the G3 standard of the facsimile, and a number of signal processing ICs are needed. Therefore, the number of installing steps increases and a satisfactory apparatus is not yet obtained in terms of the manufacturing cost and reliability.
On the other hand, as a construction to reduce the number of signal processing ICs and to reduce the number of installing steps, a construction of the matrix wiring connection has conventionally been used.
On the other hand, there has also been performed an experiment to cheaply provide an image reading apparatus in which a thin film transistor was used as a switching element and an integrated structure consisting of a photoelectric converting section, a thin film transistor section, a matrix wiring section, and the like are used, thereby reducing the function of the signal processing IC and obtaining a high reading speed.
To provide an image reading apparatus in which the manufacturing cost is further reduced and the reliability is high, there has also been developed a method whereby a photoelectric converting layer in a photoelectric converting section and a semiconductor layer in a thin film transistor section are formed by the same material of amorphous silicon, and the photoelectric converting section, thin film transistor section, matrix wiring section, and the like are integrally formed on the same substrate by use of the same manufacturing process.
Such conventional examples of image reading apparatuses are shown in FIGS. 1(A), 1(B), 1(C), and 2.
FIG. 1(A) is a schematic plan view showing one of 1728 sets each comprising a photoelectric converting section, a capacitor section, a thin film transistor section, and a matrix wiring section and showing a corresponding one of 1728 pixels arranged in the longitudinal direction.
FIGS. 1(B) and 1(C) are vertical sectional views taken along the line P--P' and Q--Q' in FIG. 1(A), respectively.
FIG. 2 is a cross sectional view of one pixel of the conventional image reading apparatus.
For easy understanding, FIG. 2 is diagrammatically illustrated in a simple form and there is no strict corresponding relation with FIG. 1(A).
In FIG. 1(A), a photoelectric converting section 1 has a lower electrode 8 also serving as a light shielding film for a light from the side of a substrate. The light irradiated from the substrate side passes through a light passing window 7 and is reflected by the surface of an original (not shown) at a position which is vertically located over the drawing. The scattered light enters the photoelectric converting section 1. A photo current induced by generated carriers flows through an accumulating capacitor section 2 and is accumulated. The accumulated charges are fed to a matrix wiring section 5 having signal lines by a thin film transistor section 3, and sent to a signal processing section (not shown).
A thin film transistor section 4 functions to discharge the charges remaining in the capacitor after the charges were transferred and to return the capacitor to an initial value.
In FIG. 2, a construction of the layer of each section will be briefly explained. In the diagram, reference numeral 1a denotes a photoelectric converting section; 2a is an accumulating capacitor section; 3a is a thin film transistor section; and 5a is a matrix wiring section. These sections have a common layer structure of five layers comprising: first conductive layers 11-1, 11-2, 11-3, and 11-4; an amorphous silicon nitride layer 12; an amorphous silicon layer 13; an n.sup.+ amorphous silicon layer 14 for ohmic contact; and a second conductive layer 15.
On the other hand, in the case of manufacturing such an image reading apparatus, when a semiconductor layer exists between respective pixels, a crosstalk occurs due to a leakage current and it is difficult to accurately read an image. Therefore, the elements are separated by etching or the like during the manufacturing processes, thereby eliminating the unnecessary conductor together with the insulative layers.
However, such an image reading apparatus in which the elements are separated has the following problems.
When the conventional image reading apparatus is subjected to durability tests of high temperatures and high humidity, a phenomenon such that the wiring is short-circuited occurs. This phenomenon will be described with reference to FIGS. 1(B) and 1(C). Many short-circuited portions appear in the photoelectric converting section in FIG. 1(A) and in the matrix wiring section in FIG. 1(B). In these structures, a high electric field (potential difference of a few V to tens of V) is applied between an upper electrode A and a lower electrode B. When the apparatus is subjected to the durability tests of high temperatures and high humidity in this state, an electrochemical reaction occurs between the electrodes A and B through a water component and ions (indicated by arrows in the diagram) which enter from the outside through an interface between a passivation film C made of, for example, polyimide or the like and a substrate D made of, for example, glass or the like. A corrosion of the electrodes in these portions progresses and this results in the short-circuit between the electrodes A and B. Those problems are ones concerned with the contact type photoelectric conversion apparatus comprising an electric circuit and directly contacting an original containing moisture, and should be solved.